This invention relates to the removal and recovery of condensable vapors from a gas stream. Many industrial processes produce gas streams containing condensable vapors, such as water vapor and volatile organics. Typically, it is desirable to remove and recover these condensable vapors from the gas stream for environmental or economic reasons.
Processes for removing condensable vapors from gas streams are known. Merten, in U.S. Pat. No. 4,466,202, discloses a process for separating a condensable gas from a non-condensable gas by preferentially passing the vapor through a semipermeable membrane. The condensable gas is then compressed using a vacuum compressor and subsequently condensed in a heat exchanger, permitting the recovery of the condensate, as well as recovery of the latent heat of condensation. However, the use of a vacuum compressor makes this process somewhat energy-intensive, and requires high capital costs for the vacuum compressor. Baker, in U.S. Pat. No. 4,553,983 discloses essentially the same process for recovering and concentrating organic vapors from a feed stream of air having an organic vapor concentration of no more than 20,000 ppm by volume. This process suffers from the same drawbacks.
The use of refrigeration to condense a vapor from a feed gas stream is well known in the art. Feed gas is compressed and cooled below the dewpoint of the condensable component of the feed gas. However, the removal efficiency of this process is limited since the dewpoint of the feed gas can only be cooled to the temperature of the cooling medium used in the refrigeration system. Wijmans, in PCT Application No. WO 91/06363, discloses a hybrid process combining refrigeration/condensation with the membrane process discussed above. Although the hybrid process is an improvement on the individual processes, it still suffers from the same inherent drawbacks as the membrane process.
It is therefore an object of the present invention to provide an improved method for removing and recovering a condensable vapor from a gas stream simply and efficiently without the use of compressors. This object and others are met by the present invention, which is summarized and described in detail below.